1. Field of the Invention
The present invention relates to a motor-driven supercharger having an electric motor built-in.
2. Description of the Related Art
To supply an air having a density increased by a compressor to an engine is called supercharging, and a structure providing for a driving work of the compressor on the basis of an exhaust energy is called as an exhaust-gas turbocharger.
The exhaust-gas turbocharger is generally constituted by a compressor and a turbine which are arranged so as to sandwich a bearing unit therebetween. The compressor has a compressor impeller built-in, and the turbine has a turbine impeller built-in, respectively. The compressor impeller and the turbine impeller are coupled to each other by a connecting shaft (a shaft) supported by a bearing unit, and are structured such as to rotationally drive the turbine impeller on the basis of an exhaust gas of the engine, transmit the rotating force to the compressor impeller via the connecting shaft, and compress the air by the compressor impeller so as to supercharge to the engine.
In the exhaust turbine supercharger mentioned above, there has been already proposed a structure having an electric motor built-in for assisting an acceleration at a time of rotating at a low speed (for example, patent documents 1, 2 and 3). Hereinafter, the exhaust-gas turbocharger having the electric motor built-in mentioned above is simply called as “motor-driven supercharger”.
The motor-driven supercharger in the patent document 1 is provided with an electric motor (a stator 51 and a rotor 52) rotationally driving a rotor. The rotor is constituted by a turbine impeller 53, a compressor impeller 54, a shaft 55 coupling them and a spacer collar 56 to which the rotor 52 of the electric motor is attached. The shaft 55 is supported by a single semi-floating bearing 57. The semi-floating bearing 57 has a hub 53a of the turbine 53 and thrust surfaces 57a and 57b engaging with the spacer collar 56.
In accordance with this structure, a thrust force applied to the rotor is supported by the hub 53a of the turbine of the semi-floating bearing 57 and the thrust surfaces 57a and 57b engaging with the spacer collar 56.
The motor-driven supercharger in the patent document 2 has a rotor 62 supported by an extension portion in an axial direction of a compressor wheel 61, and a stator 64 supported by a housing 63 so as to be spaced to an outer side in a radial direction from the rotor 62, as shown in FIG. 2.
The motor-driven supercharger in the patent document 3 has the following structure as shown in FIG. 3. A shaft 74 in which a compressor wheel 75 is coupled to one end is rotatably supported in an inner portion of a center housing 71. A compressor housing 72 and a turbine housing 73 are coupled to both sides of the center housing 71 by bolts 82 and 83. An electric motor cartridge 76 is fixed to an inner portion of the center housing 71. The electric motor cartridge 76 is constituted by a first cartridge housing portion 78, a second cartridge housing portion 79, a rotor 79 and a stator 80. The electric motor cartridge 76 can be produced independently from a step of installing to the motor-driven supercharger. The electric motor cartridge 76 is fixed to the center housing 71 by a cartridge screw 81. Further, a water cooling jacket 71a is formed in a portion surrounding the electric motor cartridge 76 in an inner portion of the center housing 71.
Patent Document 1: U.S. Pat. No. 6,449,950
Patent Document 2: U.S. Pat. No. 6,032,466
Patent Document 3: Japanese Unexamined Patent Publication Translated Version No. 2006-514526
In the motor-driven supercharger, since the compressor impeller and the turbine impeller coupled by the shaft is rotatably driven by the built-in electric motor, it is necessary to firmly fix the stator (the motor stator) of the electric motor receiving a reaction force to the casing.
However, in the case that the stator 51 is gripped by two electric motor casings 58a and 58b from both sides in an axial direction such as the motor-driven supercharger in the patent document 1, the additional casings 58a and 58b are necessary in comparison with the conventional supercharger which does not have the electric motor built-in. Further, since the compressor impeller is close to the stator of the electric motor, there is a problem that it is hard to cool both the compressor impeller and the electric motor.
In the same manner, in the motor-driven supercharger in the patent document 2, in order to have the stator 64 of the electric motor built-in, an exclusive fixing part such as a clamping bracket 65 fixing the additional casing 63 and the stator 64 is necessary. Further, in this embodiment, since the water cooling jacket 66 is provided within a wall portion of the casing 63, the structure of the casing 63 becomes complicated.
In the motor-driven supercharger in the patent document 3, any structure corresponding to the additional casing is not provided, and the structure is made such that the electric motor cartridge 76 is installed as an integral part to the center housing 71. However, in order to fix the electric motor cartridge 76 to the center housing 71, it is necessary to use an exclusive fixing part such as a cartridge screw 81. Further, since the water cooling jacket 71a is provided within a wall portion of the center housing 71, it is necessary to form the water cooling jacket 71a of the center housing 71 by a casting or the like, and a structure thereof becomes complicated. Further, since the structure is made such as to cool the electric motor cartridge 76 via a wall portion of the center housing 71 in place of directly cooling the electric motor cartridge 76 by the water cooling jacket 71a, a cooling efficiency is not good.